Fan and method for operating a fan

ABSTRACT

The invention relates to a fan, particularly a radial fan, having a fan hub with a rotational axis. A plurality of fan blades is disposed about the rotational axis for deflecting an air flow. The invention provides that an adjustment device is provided at the fan blades for the rotational speed-dependant adjustment of an air flow.

PRIOR ART

The invention is based on a fan and a method for operating a fan asgenerically defined by the preambles to the independent claims.

It is generally known in electric power tools to use fans, especiallyradial and semiaxial fans. Because of sometimes excessive idling rpmbecause of an overly low fan moment in idling, interfering vibration ofthe electric power tool can occur or be increased, which among otherthings reduces the brush service life of the electric motor andcontributes to increased material fatigue.

The fan in an electric power tool performs the task first of cooling thethermally stressed components in the electric power tool, and second, ofregulating the idling rpm of the motor by means of a suitable idlingmoment. In a universal motor, for instance, by means of a fan disposedon the armature shaft, the universal motor is protected againstuncontrolled revving during idling. A low load moment is also created bysupporting the armature shaft at the bearing points; in comparison tothe load moment from the fan, however, the load moment from the bearingis low. In an electrical appliance, such as a vacuum cleaner, the airflow fed by the fan is employed, for instance being aspirated.

In idling, that is at high rpm without work being drawn at the spindle,the electric power tool is sufficiently well supplied with cooling air.At the same time, noise emissions and the vibration load on thecomponent structure both increase because of the high rpm.

DISCLOSURE OF THE INVENTION

The invention is based on a fan, in particular a radial fan, having afan hub and a rotational axis, in which a plurality of fan blades fordeflecting an air flow are disposed around the rotational axis.

It is proposed that an adjusting device be provided for rpm-dependentadjustment of an air flow at the fan blades.

The air flow at the fan blades can be varied, both by the fan bladesthemselves and additionally, or alternatively, by suitable fixtures inthe fan.

As a result, different goals can be attained. On the one hand, as afirst alternative, with increasing rpm of the fan drive, it is possibleby a suitable adjustment of the air flow to increase the moment of thefan to beyond the normal rpm-dependent moment characteristic resultingwhen adjustment is not done. On the other hand, as a second alternative,with decreasing rpm of the fan drive, it is possible by a suitableadjustment of the air flow to improve the flowthrough behavior of thefan and as a result, at low rpm, or in other words as a rule under heavyload, an increased ratio—compared to a normal rpm-dependent flowthroughcharacteristic without adjustment—can be established between the volumeflow and the rpm. The concrete embodiment of the adjusting device maydiffer for the first and the second alternatives.

Fundamentally, the fan can have fan blades that are curved forward orbackward, or uncurved fan blades.

Advantageously, the knowledge that the work conversion in radial fans,and thus the fan moment, depend primarily on the exchange of impetusbetween the fan flow and its blade geometry can be exploited.Preferably, the fan is used in an electric power tool or an electricalappliance, such as a vacuum cleaner, and is driven by the electric motorthereof. A strong deflection of the flow in the fan and a high air flowrate produce a high torque at the shaft of the motor (in this case theelectric motor). Correspondingly, a slight flow deflection or a lesserair flow rate produces a lesser torque. The flow deflection can bevaried by the fan blades themselves, or additional elements may beprovided that vary the air flow as a function of rpm. The flowdeflection by the fan blades can be accomplished passively, for instancevia flexible regions of the fan blades, and/or via an active controlmechanism that acts on the fan blades.

In the second alternative, it is favorable if the adjustment of the airflow is done such that at low rpm, for instance at an operating pointunder load of the tool/appliance cooled by the fan, a lesser flowdeflection takes place than at higher rotary speeds, for instance inidling, specifically in such a way that at low rotary speeds, thegreatest possible air flow is delivered. The flow deflection can be donefor instance with fan blades, in particular with additional adjustingmechanisms in the fan blades. The flow deflection can be achieved bymeans of flaps, for instance.

With the increase in the rpm of the fan and thus of the motor shaft ofthe electric motor by which the fan is preferably driven, thecentrifugal force acting on the fan structure increases as well.

It is also advantageous that the adjustment of the air flow, in thefirst alternative, can be done such that at high rpm an adequate loadmoment, which with an unvaried air flow would be less, acts on the motorshaft. In the second alternative, at lower rotary speeds, an increasedratio between the volume flow in the rpm can be established, for optimalcooling performance. Favorably, it can be possible to make the reductionin the volume flow less dependent on the rpm reduction of the electricmotor.

Given a suitable adjustment in the first alternative, the resulttogether with the centrifugal force and the fluid force, that is, theforce that is exerted by the air flow, and given a suitable embodimentof the fan blades, leads to a suitable deformation of the fan blades andto an increase in the flow direction, to an increase in the fan moment,and to a reduction in the idling rpm. Because of the lesser bladedeformation at the operating point (that is, at a lesser rpm), there area lesser flow deflection and a lower fan torque, and thus better overallefficiency of an electric power tool in which the fan is disposed.

Favorably, a region that is deformable by centrifugal force and/or fluidforce in at least one of the fan blades can form a component of theadjusting device. Preferably, the fan blade, along its longitudinalchord, can be connected at least in some regions to the fan hub, whichis also known as the bottom plate of the fan blades, and can be separatefrom the fan hub in some regions. Alternatively or in addition, it isalso conceivable that the fan blades can be connected in at least someregions on a fan cover disk that rotates with them and can be separatein some regions. The fan cover disk is located facing the fan hub insuch a way that the fan blades are disposed between the fan cover diskand the fan hub.

Depending on the effect desired, various provisions are possible, whichone skilled in the art will select to suit. In the case of a forwardcurvature of the fan blade, its region near the circumference can beconnected to the hub and/or the fan cover disk. In the case of arearward curvature of the fan blade, its region near the rotational axisand/or its region near the circumference can be connected to the fan huband/or the fan cover disk. The attachment of the fan blades ispreferably not continuous; instead, at least one interruption isprovided.

Advantageously, in the unconnected region the fan blade can be embodiedas more flexible than in the connected region. However, it can also beembodied flexibly throughout.

Because of the lesser blade deformation at the operating point (that is,at a lesser rpm), there are a lesser flow deflection and a lower fanmoment, and thus better efficiency of an electric power tool orelectrical appliance in which the fan is disposed. As a result of theutilization of the fluid and centrifugal forces, which are alwayspresent, additional fittings, such as an active mechanical adjustingmechanism in the electric power tool or electrical appliance, can bedispensed with.

In the preferred passive variable-rpm blade deformation in preferredradial fans, for regulating the operating performance of electric powertools, an adaptation of the fan characteristic of the radial fan canadvantageously be achieved by means of passive blade deformation,utilizing the incident fluid and centrifugal forces for optimizing theoperating performance of electric power tools. In a favorable way, inthe first alternative, the idling rpm can be reduced, and as aconsequence, component vibration can be lessened. This also increasesthe brush service life in the AC range and postpones fatigue in thematerial. Noise emissions from the preferred electric power tool can bereduced as well.

In addition to fan blades, movable elements which vary the air flow as afunction of rpm can be provided on the fan hub and/or on the fan coverdisk. This is especially preferred in the second alternative.

The fan blades can additionally be adjustable, or can also be embodiedrigidly. These movable elements, preferably flaps, can change theirposition as a function of the centrifugal force of the fan. The flapsmay be an integral component of the fan, or separate components that aredisposed on the fan. Thus at low rpm, the embodiment can be such that anoptimal air flow guidance takes place, with a corresponding high airflow. At higher rotary speeds, by greater deformation or adjustment ofthe flaps and correspondingly adequate blocking of the cross sectionand/or a favorable deflection of the flow, a lesser air flow can bedelivered.

Favorably, alternatively or in addition, a separate device from the fanhub and/or the fan cover disk, for adjusting the fan blades, may beprovided, for instance in a manner known in exhaust gas turbochargers orfor the adjustment of the rotor blades of a helicopter.

It is even conceivable to combine the first and second alternatives withone another, if active air quantity control can be done by means of aregulator and/or controller. By active adjustment of the firstalternative and/or of the second alternative, the flow geometry of thefan can be designed favorably for every instance of operation. Forinstance, the fan could first be operated by the first alternative, thatis, at increased fan moment at high rpm. In a load situation (lesserrpm), the air quantity decreases, until such time as the motortemperature, after a brief time, has risen so much that more cooling airis needed. A switch could then be made over to the second alternative,which in the load situation makes a high cooling air flow possible.Expediently, an adjustment, for instance active adjustment, of the airflow at the fan blades and/or at movable flaps could then be provided,via actuators.

A method for operating a fan is proposed, in which an air flow at thefan blades is varied as a function of rpm in such a way that at highrotary speeds, a higher moment of the fan is established, compared to anrpm-dependent moment characteristic without adjustment. This is apreferred mode of operation in accordance with the first alternative.

In accordance with the second alternative, a method for operating a fanis proposed in which an air flow at the fan blades is varied as afunction of rpm in such a way that at low rotary speeds, a greater ratiobetween volume flow and rpm is established than at high rotary speeds.

The invention can advantageously be employed in radial fans or semiaxialfans, which axially aspirate an air flow and radially or semiaxiallyoutput cooling air. The invention can also be employed in axial fans,which axially aspirate an air flow and axially output it.

The invention can be used especially advantageously for electric powertools having motors or universal motors that have a fan, or in generalin fans that are used for cooling motors. However, since electric powertools typically have a fan, the invention, such as the principle ofpassive blade deformation, can advantageously be employed in anyelectric power tool with a suitably high motor rpm, given suitable fangeometry.

BRIEF DESCRIPTION OF THE DRAWINGS Drawing

Further advantages will become apparent from the ensuing description ofthe drawings. In the drawings, exemplary embodiments of the inventionare shown. The drawings, description and claims include numerouscharacteristics in combination. One skilled in the art will expedientlyconsider the characteristics individually as well and put them togetherto make useful further combinations.

FIGS. 1 a-1 c show a perspective view of a rearward-curved preferred fanwith a plurality of fan blades (FIG. 1 a), a detailed view with internalattachment of one fan blade to the fan hub (FIG. 1 b), and a detailedview with external attachment of one fan blade to the fan hub (FIG. 1c);

FIGS. 2 a, 2 b show a perspective view of a forward-curved preferred fanwith a plurality of fan blades with external attachment to a fan hub(FIG. 2 a) and a detailed view with external attachment of one fan blade(FIG. 2 b) to a fan hub;

FIGS. 3 a-3 c show an effect of a resultant force on a rearward-curvedfan blade with internal attachment (FIG. 3 a) and with an externalattachment (FIG. 3 b) to a fan hub, and an effect of a force on aforward-curved fan blade with external attachment to a fan hub (FIG. 3c);

FIGS. 4 a, 4 b show a plan view on a detail of a preferred fan withmovable flaps (FIG. 4 a) and a side view of a movable flap at variousrotary speeds (FIG. 4 b).

EMBODIMENTS OF THE INVENTION

In the drawings, functionally identical or identically acting elementsare each identified by the same reference numerals. The figures areschematic illustrations of the invention. They do not show specificparameters of the invention. Furthermore, the figures show only typicalfeatures of the invention and are not intended to limit the invention tothe features shown.

For explaining the invention, FIGS. 1 a-1 c and 2 a, 2 b show a fan 10with a fan hub 18. A plurality of fan blades 12 for deflecting an airflow is disposed on the fan hub 18 about a rotational axis 14. Theinflow direction of the air flow is in the axial direction in the centerregion 16 of the fan hub 18. A shaft, not shown, is disposed at thecenter of the center region 16. For the sake of simplicity, no coverdisk is shown, since it would conceal the fan blades 12. However, it isunderstood that it can be present and can be connected to the fan blades12 in a way comparable to what is described below for the fan hub 18. Afan cover disk of this kind is known in the most various versions, forinstance with or without exit-side deflection of the flow in thecircumferential region of the cover disk. The cover disk may also besolidly connected to the fan blades 12 and rotate with them. The fanblades 12 can also be fully attached in their length to the cover diskand attached only partly to the fan hub 18, so that they protruderadially past the fan hub 18.

FIGS. 1 a through 1 c show rearward-curved fan blades 12, whileforward-curved fan blades 12 are shown in FIGS. 2 a, 2 b. The directionof rotation is clockwise, as an example.

According to the invention, an adjusting device 26, 28 for rpm-dependentadjustment of an air flow is provided at the fan blades 12. The fanblades 12 can be connected to the fan hub 18 in the region 16 near thecenter of the fan hub 18, or in the region of its circumference. Theunconnected regions of the fan blades 12 can deform under the influenceof centrifugal force and of the fluid force, that is, the pressureexerted by the air flow. Advantageously, these regions can be embodiedin flexible fashion.

A region 26 a (near the circumference) or 28 a (near the center) of thefan blades 12 that is deformable by centrifugal force and fluid forceforms a component of the adjusting device 26, 28. The fan blades 12,along their longitudinal chord 20, can be connected at least in someregions to the fan hub 18 and separate at least in some regions from thefan hub 18.

In the case of a rearward curvature of the fan blade 12, an attachment30 of its regions 28 a near the rotational axis (FIGS. 1 a and 1 b) or a(partial) attachment 32 of its regions 26 a near the circumference (FIG.1 c) on the fan hub 18 is provided.

In the case of a forward curvature of the fan blades 12, an attachment32 of their regions 26 a near the circumference to the fan hub 18 isprovided, as can be seen in FIGS. 2 a, 2 b. In the vicinity of the outercircumference, the fan blades 12 are connected (attachment 32) to thefan hub 18, while the region near the center of the fan blades 12 isdetached from the fan hub 18.

Depending on the whether the fan 10 is optimized to an increased fanmoment at high rotary speeds or increased overall efficiency of theelectric power tool or electrical appliance (first alternative), or toan increased ratio between the cooling air flow and the rpm at lesserrotary speeds (second alternative), the fan blades 12 and the fan 10should be designed correspondingly suitably so as to attain theapplicable goal in combination with the rpm-dependent deformation of thefan blades 12 or with an expedient adjusting mechanism in the secondalternative.

When there is little space in the tool, additional fixtures foradjusting the fan blades or air flow can be dispensed with. Adapting thegeometry to adapt the flow guidance can be done passively by anintentional, variable-rpm blade deformation on the basis of theelasticity of the material of the radial fans, utilizing fluid andcentrifugal forces. If space is adequate, active blade adjustment(mechanical adjusting mechanism) can in principle also be done. With theincrease in the rpm, the centrifugal force acting on the fan structurerises. Along with the fluid force, and given suitable blade attachmentto the fan hub and/or fan cover disk, this leads to a deformation of thefan blades and an increase in the flow deflection, an increase in thefan moment (beyond the normal rpm-dependent moment characteristic), andthe reduction of the idling rpm. As a result of the lesser bladedeformation of the operating point (lower rpm), a lower fan moment(lesser flow deflection) and better overall efficiency of the electricpower tool result.

FIGS. 3 a through 3 c show a position of the fan blades 12 at equalrotary speeds and under the influence of centrifugal and fluid forces.Position 12 a corresponds to undeformed fan blades 12. The deformationof the fan blades 12 in the unconnected regions is clearly visible; arearward-curved fan blade 12 with internal attachment, that is near thecenter, to the fan hub, not shown, in FIG. 3 a and with an externalattachment, that is, near the circumference, to a fan hub in FIG. 3 b isshown. FIG. 3 c shows a forward-curved fan blade with externalattachment to the fan hub, not shown.

In addition to the fan blades 12, which can optionally be rigid ordeformable, movable elements 40 can be provided on the fan hub 18, whichvary the air flow as a function of rpm. This variant is especiallypreferred in the second alternative. FIG. 4 a shows a plan view on apreferred fan 10 (the fan blades are not shown), in which the elements40, embodied for instance as flaps, are provided in the manner oftongues stamped halfway out of the fan hub 18. FIG. 4 b shows a sideview of the fan 10. It can be see how at low rotary speeds, an air flowL1 is relatively weakly deflected by the element 40 embodied as a flap.In this state, the air flow L1 is delivered optimally.

At higher rotary speeds, the element 40 a embodied as a flap liftssomewhat away from the fan 10 and deflects the air flow L2 more stronglythan at lower rotary speeds. In this case, the flap causes the air toleave the fan 10 sooner.

With the provisions shown for the first alternative, the idling rpm ofan electric power tool or electrical appliance can advantageously bereduced. This can be achieved by means of a greater deflection of theair flow in the idling mode of the electric power tool. At the sametime, in the operating points of the tool or appliance (lower rpm), goodoverall efficiency can be attained.

The mode of operation of the second alternative can be explained inconjunction with a vacuum cleaner, as an example. In the normaloperating mode, the fan of a vacuum cleaner delivers a certain quantityof air, which should be as large as possible to make good vacuumingpossible. If the vacuum cleaner sticks to a surface an air flow can nolonger be aspirated, then the rpm of the fan rises, since air is nolonger being delivered and power is no longer being demanded from thedriving electric motor. The operating behavior of the fan in this rangeof high rotary speeds in the second alternative now has the effect thatthe suction of the vacuum cleaner is weaker, and the vacuum cleaner caneasily be freed from the surface. The rpm then drops again, since aircan be aspirated again. As a result of the operating behavior at lesserrpm in the second alternative, the air flow can increase again, andvacuuming can continue in the normal fashion.

1-12. (canceled)
 13. A fan, in particular a radial fan, having a fan hubwith a rotational axis, a plurality of fan blades disposed on the fanhub for deflecting an air flow about the rotational axis, and anadjusting device provided on the fan blades for rpm-dependent adjustmentof an air flow.
 14. The fan as defined by claim 13, wherein a region,deformable by centrifugal force and fluid force, of at least one of thefan blades forms a component of the adjusting device.
 15. The fan asdefined by claim 14, wherein the fan blade, along a longitudinal chordthereof, is connected at least in some regions to the fan hub and/or toa fan cover disk and is separated in some regions from the fan huband/or from the fan cover disk.
 16. The fan as defined by claim 14,wherein in a forward curvature of the fan blade, a region thereof near acircumference of the fan hub, is connected to the fan hub and/or to afan cover disk.
 17. The fan as defined by claim 15, wherein in a forwardcurvature of the fan blade, a region thereof near a circumference of thefan hub, is connected to the fan hub and/or to the fan cover disk. 18.The fan as defined by claim 14, wherein in a rearward curvature of thefan blade, a region thereof near the rotational axis and/or a regionthereof near a circumference of the fan hub is connected to the fan huband/or to a fan cover disk.
 19. The fan as defined by claim 15, whereinin a rearward curvature of the fan blade, a region thereof near therotational axis and/or a region thereof near a circumference of the fanhub is connected to the fan hub and/or to the fan cover disk.
 20. Thefan as defined by claim 14, wherein the fan blade in separated regionsis embodied as more flexible than in connected regions.
 21. The fan asdefined by claim 15, wherein the fan blade in separated regions isembodied as more flexible than in connected regions.
 22. The fan asdefined by claim 16, wherein the fan blade in separated regions isembodied as more flexible than in connected regions.
 23. The fan asdefined by claim 17, wherein the fan blade in separated regions isembodied as more flexible than in connected regions.
 24. The fan asdefined by claim 18, wherein the fan blade in separated regions isembodied as more flexible than in connected regions.
 25. The fan asdefined by claim 19, wherein the fan blade in separated regions isembodied as more flexible than in connected regions.
 26. The fan asdefined by claim 13, wherein in addition to fan blades at the fan huband/or a fan cover disk, movable elements are provided, which vary theair flow as a function of rpm.
 27. The fan as defined by claim 25,wherein in addition to fan blades at the fan hub and/or the fan coverdisk, movable elements are provided, which vary the air flow as afunction of rpm.
 28. The fan as defined by claim 13, wherein a deviceseparate from the fan hub is provided for adjusting the fan blades. 29.A method for operating a fan as defined by claim 13, which includesvarying an air flow at the fan blades as a function of rpm in such a waythat at high rotary speeds, a higher moment of the fan, compared with anrpm-dependent moment characteristic, is established without adjustment.30. A method for operating a fan as defined claim 13, which includesvarying an air flow at the fan blades as a function of rpm in such a waythat at low rotary speeds, a higher ratio between a volume flow and therpm of the fan is established than at high rotary speeds.
 31. Anelectric power tool having a fan as defined by claim
 13. 32. Anelectrical appliance having a fan as defined by claim 13.